If you're a science hobbyist you probably don't have access to actual liquid nitrogen (-320 degrees Fahrenheit) but you can make your own cryo-fluid from dry ice and rubbing alcohol that goes down to -110 degrees Fahrenheit, enough to instantly freeze flowers, cherries, and other popular liquid nitrogen demonstrations.

Amateur scientist weblog AmaSci demonstrates creating this cryo-fluid in the above video using soda bottles to contain the extremely cold liquid. You'll cut the top from a 2-liter and 20-oz soda bottle and poke many holes in the bottom of the smaller 20-oz bottle. Fit the smaller bottle in the larger bottle "chamber" and add chunks of dry ice all along the outside, at least two-inches high on all sides and then pour enough 99% isopropyl rubbing alcohol to saturate the dry ice. The extremely cold liquid will enter the smaller chamber via the holes and you can then use a pair of metal tongs to lower flowers, leaves, and other small items inside where they will almost instantly freeze. If you can't get dry ice pellets, you'll have to break it apart with a hammer and chisel into small chunks.

This experiment can be dangerous if you do something dumb like stick your finger in the -110 F cryo-fluid so this probably isn't for you if you're accident prone. The cryo-fluid will stick to your hands like napalm instead of evaporating like real liquid nitrogen. I'd also use something heavy to support the bottom of the 2-liter pop bottle—that is not a spill I'd want to clean up. If you're a science teacher, though, this might be for you.